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- // 后台执行:
- dispatch_async(dispatch_get_global_queue(0, 0), ^{
- // something
- });
- // 主线程执行:
- dispatch_async(dispatch_get_main_queue(), ^{
- // something
- });
- // 一次性执行:
- static dispatch_once_t onceToken;
- dispatch_once(&onceToken, ^{
- // code to be executed once
- });
- //单例的应用
- + (instancetype)sharedInstance
- {
- static id sharedInstance = nil;
- static dispatch_once_t onceToken;
- dispatch_once(&onceToken, ^{
- sharedInstance = [[self alloc] init];
- });
- return sharedInstance;
- }
- // 延迟 2 秒执行:
- double delayInSeconds = 2.0;
- dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
- dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
- // code to be executed on the main queue after delay
- });
- dispatch_queue_t 也可以自己定义,如要要自定义 queue,可以用 dispatch_queue_create 方法,示例如下:
- dispatch_queue_t urls_queue = dispatch_queue_create("blog.devtang.com", NULL);
- dispatch_async(urls_queue, ^{
- // your code
- });
- dispatch_release(urls_queue);
- 另外,GCD 还有一些高级用法,例如让后台 2 个线程并行执行,然后等 2 个线程都结束后,再汇总执行结果。这个可以用 dispatch_group, dispatch_group_async 和 dispatch_group_notify 来实现,示例如下:
- dispatch_group_t group = dispatch_group_create();
- dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{
- // 并行执行的线程一
- });
- dispatch_group_async(group, dispatch_get_global_queue(0,0), ^{
- // 并行执行的线程二
- });
- dispatch_group_notify(group, dispatch_get_global_queue(0,0), ^{
- // 汇总结果
- });
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